1. Field of the Invention
Apparatuses consistent with the present invention relate generally to an injection molding apparatus and, more particularly, to an injection molding apparatus capable of minimizing cracks at the corners of a mold.
2. Description of the Related Art
Recently, the technologies of rapidly heating or cooling a mold in the molding process in order to reduce a molding time and simultaneously produce a good molding have been proposed in the mold field.
As an example, a mold disclosed in Japanese Patent Publication No. 2001-18229 is designed to alternately introduce a heating medium and a cooling medium into a channel in the mold, thereby rapidly heating or cooling the mold. When fused resin is injected into the mold, the fluidity of the fused resin is increased by rapidly heating the mold to increase the temperature of the mold. Thereby, the resin is easily injected and a weld line is not formed in the molding. Further, after the fused resin is injected, the mold is rapidly cooled to reduce a solidification time, and thus a formation cycle is reduced.
However, because the mold is rapidly heated and then cooled in the molding process, high tensile stress repeatedly acts on corners of the mold, so that the corners of the mold undergo cracking. In other words, because the force is greatly applied from the inside to the outside of the mold by means of injection pressure and thermal expansion of the fused resin when the mold is heated, the high tensile stress is applied to the corners of the mold. When the mold is cooled, the tensile stress of the corners of the mold is released by contraction of the resin. This phenomenon causes the cracks at the corners of the mold.